Windshield wiper boot

ABSTRACT

A windshield wiper boot made by blow moulding a thermoplastic elastomer. The selected thermoplastic elastomer advantageously does not absorb moisture and will not stick to itself, thereby obviating the need for a release agent wash. The blow moulding process results in a boot of superior finish and permits the boot to be formed with a thickened saddle area where it is fastened to a windshield wiper superstructure for connection to a wiper arm and also to carry identifying logos and the like.

This application is a continuation of application Ser. No. 07/299,365,filed Jan. 23, 1989, now abandoned.

This invention relates to what is commonly referred to in the industryas a windshield wiper boot for use in covering the superstructure of awindshield wiper so as to keep out from the joints any foreign mattersuch as snow, ice or dirt.

Conventionally, windshield wiper boots consist of a longitudinal,seamless, tubular envelope conforming to the shape of a wiper and openat both ends for stretching and sliding over a wiper superstructure tobe contained in the boot. Such boots are predominantly made of a latexdipped neoprene material using a relatively costly process known as dipmoulding.

The latex material can be stretched to facilitate its installation onthe wiper blade and, because of the nature of the manufacturing process,the wiper boot has a uniform wall thickness. The chosen thickness is acompromise between a need for strength at the centre where fastenersassociated with the superstructure pass through openings in the boot,and a preference for a light, thin covering in other parts of the boot.

Although latex has been accepted as the material of preference for bootsin the past, it has some disadvantageous features. The material absorbsmoisture and tends to "swell". If the boot is exposed to water over aprolonged and continuous period, for example, to a two or three hourrainstorm, it may absorb up to 50% of its weight in water and double oreven triple its volume. The boot then sags and touches the windshield,resulting in poor wipe quality. The absorption of moisture can beparticularly detrimental in severe climates where the wind chilltemperature outside a vehicle may be well below the freezing point.

Also, the material can not be recovered for reuse should the process ofmanufacturing the boot fail for some reason. Moreover, dip moulded latexboots are prone to surface defects and the manufacturing processrequires that vigorous quality control measures by employed to ensurethat the boots have a satisfactory appearance. One common type ofsurface defect is known as a "run" and is identified by a wavy patternformed on the boot during dipping. Another defect is identified bysurface lumps which give the boot a pitted appearance and which areformed by pre-cured lumps in the latex dip.

It will be understood that latex has a variable consistency whichbecomes firmer with aging. Thus, to avert the formation of theabovementioned surface defects, it is necessary to have an ample stockof green material and adequate facilities to age the latex, on average,over a six week period. Any changes in material supply, control, anddemand are likely to result in the formation of surface defects in theboot. In extreme circumstances, the defects may extend through thethickness of the moulded material and the final boot product will haveto be discarded entirely.

Still a further disadvantage of latex dipped boots is that adjacentlatex surfaces tend to adhere to one another so that boots will clingtogether during shipping and storage if they are not treated with arelease agent subsequent to moulding.

An object of the present invention is to provide a windshield wiper bootwhich retains the advantages of latex dipped boots and which willprovide additional advantages.

In accordance with this invention there is provided a windshield wiperassembly comprising a wiper superstructure and a blow-moulded bootcomprising an elongate substantially tubular envelope made ofthermoplastic elastomeric material covering the superstructure andadapted to shield the superstructure from weathering elements. The boothas a channel extending along the length thereof and is received in aretaining groove formed in the superstructure. A squeegee is slidablyreceived in the channel and a fitting is attached to a central portionof the superstructure by fasteners which penetrate the boot in athickened portion thereof, the fitting being adapted for attachment of awiper arm to the superstructure.

Preferably, the thermoplastic elastomer is selected from the groupcomprising: ALCRYN 6331 (trade mark of Dupont), SANTOPRENE, and GEOLAST(trade marks of Monsanto).

These and other aspects of the invention will be better understood withreference to the accompanying drawings and the following description ofembodiments of a boot made according to the invention and to a preferredmethod of making the boot.

FIG. 1 is a perspective view illustrating a wiper superstructure andsqueegee assembly covered by a latex dipped boot (prior art);

FIG. 2 is a similar view to FIG. 1 illustrating a wiper superstructureand squeegee assembly covered by a blow moulded boot made according tothe invention;

FIG. 3 is a cross-sectional view taken on line 3--3 of FIG. 2 and drawnto a larger scale to illustrate the arrangement of the squeegee in theassembly;

FIG. 4 is a perspective view of a blank for making the boot and showingthe boot after moulding and prior to trimming;

FIG. 5 is a perspective sectional view taken on line 5--5 of FIG. 4 anddrawn to a larger scale with the flash in ghost outline to show achannel portion for receiving the squeegee; and

FIG. 6 (drawn adjacent FIG. 1) is a similar view to FIG. 5 illustratingan alternative embodiment of a boot according to the invention.

Referring firstly to FIG. 1, there is illustrated a booted windshieldwiper indicated generally by the numeral 14. A boot 13 consists of alongitudinal envelope open at both ends 15, 16 and conforming generallyto the external shape of a wiper superstructure 28 which is inserted inand shielded by the boot. The ends of the superstructure are closed tocombine with the boot to seal the assembly.

As is conventional in structures of this kind, the boot is attached tothe superstructure by fasteners 30 (typically rivets) which pass througha fitting 32 and through the boot to terminate in the main yoke of thesuperstructure (not shown). The fitting 32 provides for attachment of awiper arm in conventional fashion.

A number of surface defects are present on the sides of the boot 13which is latex dipped according to a prior art method of fabrication.These defects include a wavy pattern of runs 17, pitting 18, and aco-axial streak 19. It will of course be appreciated that such defectsdetract from the appearance of the product and make it commerciallyundesirable.

In FIG. 2, there is illustrated a booted windshield wiper indicatedgenerally by the numeral 20 and having a boot 22 made by blow mouldingaccording to the invention. In the drawing, the parts of the wiper 20common to the parts of the wiper in FIG. 1 are numbered with likenumerals. Similarly to the latex dipped boot 14, the blow-moulded boot22 consists of a longitudinal envelope open at both ends 24, 26, andconforming generally to the external shape of the wiper superstructure28. A notable difference between the boots is their external appearancewhich in the case of the blow-moulded boot 22, is free from defects andsmooth except for beads 68 and 62 (not shown) more fully described inthe following description, in particular, with reference to FIGS. 4 and5.

Reference is next made to FIG. 3 which shows a typical cross-section ofthe assembly. A retaining groove 34 is provided in an elongatereceptacle 36 forming part of the superstructure, and the boot has acomplementary inwardly directed channel portion 38 in the receptable andextending about a squeegee 40 slidably retained in the assembly.

Before describing the boot 22 in further detail, the method of makingthe boot will be described with reference to FIGS. 4 and 5. Firstly, atubular parison is extruded continuously from a thermoplastic elastomersuch as ALCRYN 6331 (trade mark of Dupont) or SANTOPRENE or GEOLAST(trade marks of Monsanto) and fed into a blow moulding machine. Theparison is preferably formed with a small positive pressure of about 2psi to have a wall thickness which is at a maximum where the parison isto become the longitudinal centre of the boot and thinner at theportions corresponding to the ends of the boot. A portion of the parisonis shown in FIG. 4 after severing and blow moulding to form a blank 44from which the boot is trimmed. This Figure also serves to demonstratethe manufacturing process.

The blank 44 consists essentially of a peripheral flash 46 surroundingthe boot 22. It can be seen from a severed end 49 of the blank that ithas been formed from a continuous tubular parison which is fed from theleft as drawn in FIG. 4 into a two-part mould and entered over aninjection head 50 from which it has been removed in FIG. 4. It will beclear that the injection head 50 causes the blank to have the shapeshown at 52 and that a blow pin 54 will provide access in the mould topressurize the space within the boot 22, optionally with heated air, andcause it to take the shape of the mould. Preferably this takes place intwo blowing stages, the first stage being at a low pressure to preformthe boot and the second stage being at a high pressure to stretch thepreformed moulding and give the boot better definition and an improvedsurface finish. Portions 56, 58 of excess material are provided at theends of the boot to improve the flow of material at the ends and theseportions will be cut off at the lines indicated by the letters "A" and"B". This will give the ends 24, 26 shown in FIG. 2.

The mould is heated to bring the thermoplastic elastomer material abovethe temperature at which plastic deformation will occur without meltingit. Also in order to vary the thickness of the finished boot locally,the mould is cooled in the region of the desired thickness. Forinstance, the region corresponding to a saddle portion 60 is cooled torestrict the flow of material here. This retains some of the thickenedportion of the parison so that the resulting boot will have sufficientthickness in this region of the saddle to strengthen the boot.

After formation as shown in FIG. 4, the blank 44 is cooled below itsplastic transition temperature, vented at a vent hole 61 and the mouldhalves are separated. The boot 22 is then stripped from the blow pin 54and moved to a cooling station. To increase production in an automatedmanufacturing process, the mould clamps may be rotated on a carousel orshuttered between a clamping station and a blowing station.

After cooling, the flash 46 is pulled from the blank 44 to trim the boot22. FIG. 5 represents the finished cross-section and shows the flash 46to be removed. In an automated system, it will be clear that toolingwill be required to hold the boot in position for removing the flash andthis may include tooling which holds the boot in a deformed position toexpose the flash shown at the bottom of FIG. 5 so that it can be pulledto leave only a small bead 62 on the outside of the boot. On the upperside of the boot, the flash is similarly removed to leave a small bead68.

The parison may have a variable wall thickness as previously mentioned.This is achieved by controlling the rate of feed of thermoplasticelastomer material in the charge to form the parison. Withoutrestricting the flexibility of the thermoplastic elastomer material, thethickness of the boot may be increased to a mean thickness of 0.018inches in the centre or saddle portion 60 of the boot from a meanthickness of 0.009 inches in the remaining portions of the boot.

The material used is preferably ALCRYN 6331 because it absorbs verylittle water (max. 0.5% by weight) and because of its superiorweathering properties and also because these properties can bemaintained in a wide range of temperatures, typically from -40 degrees Cto well above normal ambient temperatures. Also, because it is elastic,it can be stretched during installation over a wide superstructure andwill resume its moulded shape when released. A further importantconsideration is that because the material is thermoplastic, it can berecycled and consequently all of the waste, flash and unacceptableproduct can be recycled and used again. This of course enhances theeconomic desirability of the process.

Finally, a particular advantage in manufacture over the previous methodis that the blow moulding process produces a product with excellentsurface qualities and can permit identification logos or names to beadded to the finished boot simply by having these identifiers in themould. Still a further advantage is that thermoplastic elastomersurfaces do not adhere to one another thereby obviating the need to washthe boot in a release agent prior to packing and shipping.

It will be understood that several variations may be made to the abovedescribed embodiment of the invention. In particular, the shape andconfiguration of the mould may be altered to facilitate the formation ofthe inwardly directed channel portion of the boot. Whereas in use, thechannel portion is inwardly directed toward the receptable 36 to receivethe squeegee 40, a boot 70 may be moulded with an outwardly directedtrough 72 which is simply deformed by pushing inwardly after moulding(FIG. 6). If this mould configuration is adopted then the parting linebetween the moulds will preferably be located to produce a laterallyextending flash 74 separating an upper portion of the boot from a lowerportion such that the trough 70 does not have the bead.

I claim:
 1. A windshield wiper assembly comprising:a wipersuperstructure; a blow-moulded boot comprising an elongate substantiallytubular envelope made of thermoplastic elastomer material covering thesuperstructure and adapted to shield the superstructure from weatheringelements, the boot having a channel extending along the length thereofand being received in a retaining groove formed in the superstructure; asqueegee slidably received in the channel; and a fitting attached to acentral portion of the superstructure by fasteners which penetrate theboot in a thickened portion thereof, the fitting being adapted forattachment of a wiper arm to the superstructure.